In the related art, in a medical field, as a treatment instrument in which a treatment unit treating for a living body tissue is arranged in a distal end of an insertion unit to be inserted into a body cavity, for example, a treatment instrument which captures a lesion such as a polyp by a snare loop is disclosed (refer to Japanese Unexamined Patent Application, First Publication No. H11-123198, Japanese Unexamined Patent Application, First Publication No. 2000-083964, and Japanese Unexamined Patent Application, First Publication No. H08-71082).
The snare loop (wire) used for each treatment instrument disclosed in Japanese Unexamined Patent Application, First Publication No. H11-123198, Japanese Unexamined Patent Application, First Publication No. 2000-083964, and Japanese Unexamined Patent Application, First Publication No. H08-71082 has a hexagonal shape which has a first bending portion, a second bending portion, and a third bending portion in the order from a distal end side of the snare loop. A proximal end side of the snare loop is tied by a connection pipe and the snare loop is inserted into a sheath so as to be advanced and retracted.
In any snare loop disclosed in Japanese Unexamined Patent Application, First Publication No. H11-123198, Japanese Unexamined Patent Application, First Publication No. 2000-083964, and Japanese Unexamined Patent Application, First Publication No. H08-71082, the length from the third bending portion to the connection pipe is the longest among a length from the first bending portion to the second bending portion, a length from the second bending portion to the third bending portion, and a length from the third bending portion to a connection pipe. In this manner, the snare loop can capture not only a small polyp but also a big polyp. It is possible to restrain operation resistance when the snare loop is pulled into the sheath.